On 2014-04-25 18:25:44 +0200, Andres Freund wrote: > On 2014-04-25 12:05:17 -0400, Tom Lane wrote: > > Andres Freund <and...@2ndquadrant.com> writes: > > > The case I am worried most about is queries like: > > > SELECT a, b FROM f WHERE f > ROW(38, 'whatever') ORDER BY f; > > > I've seen such generated by a some query generators for paging. But I > > > guess that's something we're going to have to accept. > > > > Meh ... is it likely that the columns involved in an ordering comparison > > would be so wide as to be toasted out-of-line? Such a query would only be > > fast if the row value were indexed, which would pretty much preclude use > > of wide columns. > > In the cases I've seen it it was usually used in addition to a indexable > condition, just for paging across different http requests. > > As completely ridiculous example:
> before: > postgres=# EXPLAIN (ANALYZE, BUFFERS) SELECT * FROM pg_rewrite r WHERE r > > ('x'::name, '11854'::oid, NULL, NULL, NULL, NULL); > QUERY PLAN > Just for some clarity, that also happens with expressions like: WHERE ROW(ev_class, rulename, ev_action) >= ROW('pg_rewrite'::regclass, '_RETURN', NULL) ORDER BY ROW(ev_class, rulename, ev_action); which is what is generated by such query generators - where the leading columns *are* indexed but not necessarily unique. Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers